1. Field of the Invention
The present invention relates to a computer system which moves a virtual computer or a logical partition operating on a physical computer onto a physically different computer.
2. Background Art
A virtual computer system in which a plurality of logical partitions (hereinafter, referred to as LPAR) is constructed on a single physical computer, each LPAR is regarded as an individual virtual computer, and an operating system (OS) runs on the LPAR is put into practical use. Accordingly, a single physical computer can function like a plurality of independent computers. This technology utilizes an idle resource of a server and reduction in TCO, such as reduction in power necessary for operating the server.
As a system for realizing an I/O request from the logically partitioned computer (or virtual computer), there are a system (hereinafter, referring to as an I/O emulation system) in which I/O issued from the OS (hereinafter, referred to as guest OS) on the virtual computer is received by a hypervisor once, and re-executed on an OS on which a hypervisor is running or an OS which is separately provided exclusively for execution by proxy, and a system (hereinafter, referred to as an I/O pass-through system) in which a guest OS directly requests a physical I/O device for I/O execution.
In regard to LPAR migration processing in the I/O pass-through system, in JP-A-2008-299509, a world wide name (hereinafter, referred to as WWN) of a fibre channel host bus adapter (FC-HBA) which is allocated to a virtual computer to be moved is inherited to an LPAR as a movement destination such that an access right to the same logical unit (LU) can be inherited from the LPAR as a movement destination. This system is a resolution method relating to LPAR migration of a shutdown system in which a physical computer moves when the guest OS is during shutdown.
Of the systems of migration which moves a virtual computer between different physical computers, a movement system in which movement is made in a state where a guest OS on a hypervisor is running, and a target guest OS on a physical computer as a movement destination is in a state of being continuously operable is called live migration. With the live migration, an access path from the guest OS to an LU is switched from a path which uses a physical device mounted in a physical computer as a movement source to a path which uses a physical device mounted in the physical computer as a movement destination.
In regard to changing the physical device, when an I/O processing system is an I/O emulation system, the hypervisor traps an I/O request (MMIO access) and switches the path of the I/O access in the layers of the hypervisor. When an I/O processing system is an I/O pass-through system, it is necessary that a guest OS to be migrated and a physical computer as a migration destination can access the same LU. To this end, it is necessary that, while a login to Fabric is performed by an LPAR as a movement source, a login to the same Fabric can be performed from an LPAR as a movement source. However, a simultaneous login to Fabric from two different FC-HBAs using the same WWN is not possible. Even when a logout of the FC-HBA as a movement source from Fabric and a login of the movement destination are executed sequentially, the login and logout processing with respect to Fabric request a maximum of tens of seconds.
For this reason, as migration in the I/O pass-through system, the following two methods are considered. (1) There is a method in which a guest OS running on a computer as a movement source is stopped, and a logout of WWN of FC-HBA used in a computer as a movement source is performed during this period, and a login is performed again from FC-HBA as a movement destination, thereby securing an access path to an LU before an LPAR restarts. However, when this system is executed, there is a period in which access from the OS to the disk is not possible, and live migration cannot be realized while the guest OS is continuously running.
As another system, (2) there is a system in which, while the same WWN is used in a logical layer, a different WWN is used in a physical layer. In this system, an alternative connection path to a storage is provided using FC-HBA which uses a logical WWN different from WWN in a normal state. At the time of execution of migration, the path is used temporarily to realize an I/O access. In this system, an alternative path is used to execute an I/O access only at the time of execution of live migration, and the path of WWN used in the normal state ends once. The path of FC-HBA using the logical WWN is initialized in the movement destination before LPAR is moved, and a link from the movement destination is established. Accordingly, it is possible to preliminarily secure the access path from FC-HBA as a movement destination to LU. In this case, the access path is secured preliminarily, whereby it is possible to make the time required for path construction of the I/O access independent from the downtime of the guest OS.
When the system (2) is introduced, it is necessary to correspond to Persistent Reservation command which is an exclusive command of SCSI Primary Commands-3 (SPC-3). This function is a command which is used for exclusive control in a cluster system under a path redundant configuration.
In the Persistent Reservation command, a storage controller stores WWN of a port on the FC-HBA side and Reservation Key generated on the OS side in a pair, and executes exclusive control (there may be another system). For this reason, when WWN of FC-HBA connected to the storage changes in the movement source and the movement destination, even though an LU is not excluded and an access is possible in the access from FC-HBA before the logical WWN changes, an access to LU from FC-HBA after changing to an alternative different logical WWN is not permitted and is rejected.
In the live migration, it is necessary to move a virtual computer without making the guest OS conscious of changing of a physical computer. There is a method in which the movement of the guest OS is detected, exclusive control from FC-HBA as a movement source to LU is cancelled once, the completion of the movement after movement is detected, and exclusive control is performed again before an access from FC-HBA as a movement destination to LU is performed, thereby lifting access restriction. However, in order to realize this method, a handshake with middleware or an OS, a special OS or middleware is required, and it is difficult to apply this method in an open environment which cannot be consistent from middleware to a platform.